MIG arc welding apparatus is in high vogue. U.S Pat. No. 4,079,231 is exemplary of such MIG arc welding apparatus. A troch supports a consumable wire electrode, fed to the torch by wire feeder rolls which sandwich the wire to drive it through a passage within the torch. That passage is also subjected to a shielding gas with the gas surrounding and shielding the consumable wire electrode as it exits from a contact tube. It functions to shield the arc which is established between the consumable wire electrode and a second electrode constituted by the workpiece. In that patent, the wire feeder rolls are driven by a motor whose speed is controlled by a motor governor via a control circuit. To effect welding, the operator touches the end of the consumable wire against the workpiece and this results in an instantaneous short circuit across a power supply in a sensing circuit. The sensing circuit provides a low voltage output signal which is fed to the control circuit. The control circuit produces, in turn, an output signal which energizes the welding contactor and the welding contactor produces a signal which turns on the power supply. With the power supply turned on, the arc is immediately established between the consumable wire electrode and the workpiece electrode. Also, in response to the sensing circuit output signal, the control circuit feeds a signal to the motor governor which starts the wire feeder motor. Additionally, the control circuit feeds the signal to the gas supply which initiates flow of a shielding gas to the torch. Upon establishment of the arc between the consumable wire electrode and the workpiece electrode, the output from the sensing circuit terminates. However, the flow of welding current through the cable lead to the torch and thus to the consumable wire electrode is immediately sensed by a current detector circuit, which circuit is connected to a part of the cable lead. The detector circuit produces in turn an output signal which is fed to the control circuit, and the control circuit in response to the output signal, continues to maintain the signal to the welding contactor. This keeps the power supply in circuit and also maintains the signal to the motor governor and the signal to the gas supply so that the motor drive system and the supply of inert gas continues. Thus, the wire feeder motor continues to operate and the flow of shielding gas to the torch is maintained.
Such consumable metal inert gas (MIG) arc welding is in large use because the MIG welders are faster and use less heat (amperage) for a given weld than other common welding methods so that heat distortion of the workpiece is minimal. Such conventional MIG welders may utilize storage batteries as the source of the DC are current. But in each case, the arc and drive power is electronically coupled to yield "semi-automatic" features. MIG welders are not necessarily inexpensive. Units sold under the trademark Century cost about $700 while, a MILLER SPOOLMATIC MIG welder gun alone may cost about $1000 with a further cost of $2,000 for a power source. The MILLER SPOOLMATIC requires electronic modification to a 240 volt AC (household or three-phase industrial current) to obtain a 24 volt DC non-dropping voltage current at the arc. As for the Century unit, which runs on DC batteries, the unit is too large for portability. Cost is high because drive and arc power are electronically coupled. It is designed for use almost exclusively in welding steel and the drive speed is too slow for soft metal welds, particularly aluminum. The long drive train powered by a 24 volt motor causes the Century unit to be less energy-efficient and the push drive of the consumable wire electrode tends to cause "bird-nesting" of the consumable thin wire electrode.
MIG arc welding is also known as "semi-automatic fine wire welding". The term "semi-automatic" refers to the electrical or electronic coupling of arc and drive power in an effort to stabilize the arc voltage independent of human-induced accidental variations in arc distance. In most systems, the arc power source requires expensive electronic components to achieve a "non-drooping voltage" characteristic. In some systems where auto or deep-cycle storage batteries are used as the power source, as in Century's portable MIG welding system, an expensive and wholly unnecessary electronic couple exists between the drive and the arc. The applicant has determined, and the present invention is based on, the recognition of the inherent stability of arc power when storage batteries are used for the power source. Thus, when auto or deep-cycle storage batteries are used for the arc power source, the resulting arc is so inherently stable that no electric or electronic couple to the drive power is required or desired. The applicant has determined that storage batteries are capable of such power (inherent reserve power) that any attempt at manual modification of arc distance, accidental or intentional, has no appreciable effect on arc stability; specifically on arc voltage. A fortuitous and inherently stable match in arc and power source resistances assures an inherently stable arc gap and stable arc voltage where auto or deep cycle batteries are employed as arc power source. Applicant has determined that where one might expect a manual decrease of welding gun to workpiece distance to decrease arc distance and to decrease arc voltage and a manual increase of welding gun to workpiece distance to increase arc distance and to increase arc voltage, that is in fact not ostensibly the case where, and only where, storage batteries of common auto or deep-cycle type are used as the arc power source. In fact, if the fine wire electrode should contact the workpiece electrode, as it does in initiating the arc, the reserve power of the arc is sufficient to instantaneously melt the electrode, thus opening the arc to a stable gap and initiating the weld process.
Attempts have been made to simplify the handling and feed of the consumable wire to the torch electrode nozzle assembly in such welding equipment. U.S. Pat. No. 2,909,646 uses a pistol type welding gun which is provided with a wafer cooled electrode nozzle assembly through which a shielding gas is directed to the weld area. However, the electrode wire is fed from a separate and isolated box-like structure which encloses an adjustable speed motor operatively coupled to a drive roll and a pressure roll sandwiching the wire. This requires push feeding of the wire a significant distance to the gun and through the gun nozzle assembly. A trigger switch carried on the pistol grip of the welding gun controls drive motor operation for feeding the thin wire electrode and for controlling shield gas and cooling water flow to the gun.
U.S. Pat. No. 2,490,593 describes a combined portable welding and pneumatic tool useful in repairing cracked parts or casting by welding where it is usually necessary to first form a channel pocket for the welding material where the part is cracked or requires repair, through the use of a chisel, then to deposit the welding material in the channel or pocket which is preferably done by vibrating a rod of welding material and passing an electric current of lower voltage and high amperage through the stick of welding materials. Finally, it is desirable to peen the deposited welded material to produce a smooth dense surface over the welded portion. The patent employs a simple and efficient tool which may be interchangeably used in performing the chisel, welding and peening operations. The versatile tool includes a magazine for holding a series of rods which can be successfully used for welding, incorporates a pulsating hammer, operable to impart strokes of variable force such as light strokes for peening and welding and heavier strokes for chiseling. It has a welding rod holder which comprises a collet for positively holding the welding rod during welding operations. A pulsating hammer is detachably connected to the welding rod holder with a removable shield on the holder for the hammer. A welding rod holder includes means for delivering air from the hammer to the weld and varying the air flow to provide cooling of the desired degree. A pneumatic hammer has the intensity of the hammer pulsations varied by controlling the air exhausted from the hammer. A single valve means variable controls the operation of the pulsating hammer and variably controls the flow of air to the electrode controlling means. A pneumatic hammer has the operated tool insulated to prevent arcing between the tool and the work while carrying on peening or chiseling operations via a quick detachable connection between the body of the pneumatic hammer and the welding rod or the electrode holder, to permit separate use of the hammer for peening or chiseling.
U.S. Pat. No. 2,909,646 teaches a welding tool of gun form using a pistol grip trigger mechanism for selectively initiating and shutting off the movement of the drive of the thin wire and the supply of cooling liquid and inert gas to a pistol type apparatus. U.S. Pat. No. 2,490,593 suggests the creation of a combined portable welding and pneumatic tool. U.S. Pat. No. 2,909,646 teaches isolation of the wire feed drive from the gun receiving the same, and U.S. Pat. No. 2,490,593 suggests only the decoupling of mechanisms integrating a portable welding and pneumatic tool.
It is, therefore, a primary object of the present invention to provide an accessory or attachment to an ordinary electric hand drill for effecting a low cost battery powered MIG welder utilizing the variable speed motor of the electric motor hand drill for controliing the amperage of the welder by variable speed driving of the fine wire electrode while maintaining the current source to the electric hand drill motor electrically uncoupled to the DC voltage source creating the arc without materially affecting the stability of the welding arc.
It is a further object of the present invention to provide a highly versatile, low cost portable welder as an attachment or accessory to an ordinary AC or DC electric hand drill particularly useful in forming an MIG welder which is easy to use, lightweight, and well suited to heavy or light welding. It is noteworthy that where circumstance dictates, the parallel hook-up of both arc and drive to the same batteries, that no destabilizing relationship between arc and drive is implied or in fact exists. Performance remains unaffected regardless of the existence of said circumstantial parallel circuits because the power reserve of said batteries is sufficient to maintain a stable power supply to the drive unit unaffected by the power to the arc.